Avacyn is the archangel of Innistrad. The vampire planeswalker Sorin Markov created her and tasked her with protecting the plane. The Church of Avacyn rose from the power Sorin invested in her. Avacyn's purpose is to maintain the balance on Innistrad. Without her the equilibrium between humanity and the dark forces would be broken, with the resulting extinction of humanity at hands of the vampires or werewolves and the triumph of demons over the plane. This would also mean the end of Sorin's vampire lineage.
When Sorin left the plane in the hands of his creation, the demon Griselbrand defiantly came to the Helvault and challenged Avacyn to combat. They battled for days, out of view of all but Avacyn's host, the Lunarch, Mikaeus, and his most trusted bishops. Finally, in an act of desperate effort, Avacyn used all of her remaining strength to drive Griselbrand into the Helvault. As his final act, Griselbrand threw his spear and impaled his angelic nemesis. The binding spell backlashed as she was impaled, and Avacyn was drawn into the Helvault along with the aall the trapped demons. The angel's disappearance not only endangered the humans of Innistrad, it smashed the carefully-constructed balance between humanity and the creatures of the night.
Liliana Vess visited Innistrad in the hopes of destroying Griselbrand, with whom she had made a demonic pact that would result in her soul's enslavement. To this end, she opened the Helvault by forcing an ultimatum on Thalia, its guardian. This resulted in the release of both the demons and Avacyn, seemingly restoring mankind's defence against the darkness. Liliana used the Chain Veil to kill Griselbrand permanently.
However, rumors now abound of terror falling from the skies on blood-spattered wings and nameless horrors
lurking in the shadows. Will the planeswalkers of the Gatewatch
investigate these dark mysteries?